A hybrid energy storage system with low-temperature self-heating function and a self-heating method

Abstract

The present invention discloses a hybrid energy storage system and a self-heating method with a low-temperature self-heating function. The hybrid energy storage system includes a battery and a supercapacitor connected in parallel on a bus, and the battery and the supercapacitor are connected in parallel through a bidirectional DC / DC converter, so that the battery and the supercapacitor can be charged and discharged with each other to complete the low-temperature self-heating of the battery. The present invention is applied to the field of hybrid energy storage technology, with the battery as an energy device of the hybrid energy storage system and the supercapacitor as a power device of the hybrid energy storage system. The bidirectional DC / DC converter can be controlled by pulse width modulation to enable high-frequency mutual charging and discharging between the battery and the supercapacitor to achieve low-temperature self-heating of the battery. It has the characteristics of fast temperature rise rate and high energy efficiency, and is suitable for the inherent configuration of the hybrid energy storage system, without the need to specially integrate other heating devices or dedicated circuits, so it also has the advantages of low cost and ease of use.

Description

Technical Field

[0001] The present invention relates to the technical field of hybrid energy storage, and in particular to a hybrid energy storage system with low-temperature self-heating function and a self-heating method. Background Art

[0002] Researching energy storage devices or energy storage systems with high power density and high energy density characteristics is an eternal theme in the development of energy storage technology. At present, since it is difficult to simultaneously meet the requirements of some special electrical equipment for high energy density and high power density using a single energy storage device, a hybrid energy storage system that integrates energy storage devices and power storage devices has great application value and prospects in some specific scenarios.

[0003] At present, research on hybrid energy storage systems mainly focuses on energy management and real-time power distribution of hybrid energy storage systems. Its main purpose is to give full play to the respective advantages of energy-type devices and power-type devices, so as to provide both higher power output and higher continuous energy output for electrical equipment.

[0004] However, when the hybrid energy storage system faces an ambient temperature of -20 degrees Celsius or even -40 degrees Celsius, its energy storage devices themselves can hardly exert their original charging and discharging capabilities, causing the hybrid energy storage system to lose its advantages of high power density and high energy density in low temperature scenarios. Therefore, in order to improve the low temperature performance of the hybrid energy storage system, it is necessary to develop heating technology for the hybrid energy storage system.

[0005] It can be seen from the available literature and patents that the current heating of hybrid energy storage systems mainly adopts external heating methods such as wind heating or liquid heating (the heat source is outside the energy storage device). The external heating device is heated by the energy storage system's own energy or external energy, and then the heat is transferred to the energy storage device by heat conduction or convection. This external heating method has the disadvantages of slow temperature rise rate and low energy efficiency. In addition, for battery energy storage systems, relevant scholars have proposed a method of generating Joule heat by high-frequency charging and discharging of the battery itself in recent years. The heat of this method is generated from the inside of the battery, which is an internal heating method. Since the internal heating method does not require heat conduction, it has the advantages of fast temperature rise rate and high energy efficiency. However, high-frequency charging and discharging of batteries often requires additional excitation circuits, which makes the entire system larger in size and weight. Therefore, this type of method has not been well applied in practical applications. Summary of the invention

[0006] In view of the deficiencies in the above-mentioned prior art, the present invention provides a hybrid energy storage system and a self-heating method with low-temperature self-heating function, which use lithium batteries as energy-type devices and supercapacitors as power-type devices, and have the characteristics of fast temperature rise rate and high energy efficiency.

[0007] To achieve the above-mentioned object, the present invention provides a hybrid energy storage system with low-temperature self-heating function, including a battery and a supercapacitor connected in parallel on a bus, and the battery and the supercapacitor are connected in parallel through a bidirectional DC / DC converter, so that the battery and the supercapacitor can be charged and discharged with each other, thereby completing the low-temperature self-heating of the battery.

[0008] In another embodiment, the battery surface has a temperature sensor for measuring the real-time temperature of the battery.

[0009] To achieve the above object, the present invention further provides a self-heating method for the hybrid energy storage system with low-temperature self-heating function, characterized in that it comprises the following steps:

[0010] Step 1, when the hybrid energy storage system is started, the actual temperature of the battery is obtained, and it is determined whether the temperature of the battery is lower than the preset temperature. If so, the bus is disconnected and heated, that is, step 2 is entered; otherwise, the bus is connected and the system works normally;

[0011] Step 2, determining the optimal frequency of the battery self-heating AC excitation current based on the real-time temperature of the battery;

[0012] Step 3, controlling the bidirectional DC / DC converter by pulse width modulation, so that the battery and the super capacitor perform high-frequency mutual charging and discharging, wherein the current at the battery end during the mutual charging and discharging process between the battery and the super capacitor is the battery self-heating AC excitation current in step 2, and the battery self-heating AC excitation current is controlled to an optimal amplitude during the mutual charging and discharging process between the battery and the super capacitor;

[0013] Step 4, after a preset period of time, the actual temperature of the battery is obtained again, and it is determined whether the temperature of the battery is lower than the preset temperature. If so, return to step 2, otherwise, the bus is connected and the system works normally.

[0014] In another embodiment, in step 2, the optimal frequency of the battery self-heating AC excitation current is determined based on the real-time temperature of the battery, specifically:

[0015] Define the temperature range in which the battery needs to be AC ​​self-heated, where the right end point of the temperature range is the preset temperature in step 1;

[0016] Select several temperature sampling points in the temperature range and select several different charge states of the battery. Perform the following operations for each temperature sampling point:

[0017] When the battery is at a temperature corresponding to a temperature sampling point, the impedance of the battery is tested at each frequency and each charge state within the frequency range of the AC excitation current. For each frequency, the difference in impedance at different charge states is calculated, and the frequency with a difference less than a preset value and the smallest difference is selected as the optimal frequency of the AC excitation current for the battery at the corresponding temperature sampling point.

[0018] According to each temperature adoption point and the optimal frequency of the AC excitation current corresponding to each temperature sampling point, interpolation is performed in the temperature range to obtain a battery temperature-AC excitation current optimal frequency curve;

[0019] Based on the real-time temperature of the battery and the battery temperature-AC excitation current optimal frequency curve, the optimal frequency of the current battery self-heating AC excitation current can be obtained.

[0020] In another embodiment, in step 3, the battery self-heating AC excitation current is controlled to an optimal amplitude during the mutual charging and discharging process between the battery and the supercapacitor, specifically:

[0021] During the mutual charging and discharging process between the battery and the supercapacitor, the amplitude of the battery self-heating AC excitation is gradually increased from 0. When the upper limit of the battery terminal voltage reaches the charging cut-off voltage or the lower limit reaches the discharging cut-off voltage, the amplitude of the AC excitation current is the optimal amplitude.

[0022] The present invention provides a hybrid energy storage system and a self-heating method with a low-temperature self-heating function. A lithium battery is used as an energy device of the hybrid energy storage system, and a supercapacitor is used as a power device of the hybrid energy storage system. A bidirectional DC / DC converter can be controlled by pulse width modulation to enable high-frequency mutual charging and discharging between the battery and the supercapacitor, thereby realizing low-temperature self-heating of the battery. The system has the characteristics of fast temperature rise rate and high energy efficiency, and is suitable for the inherent configuration of the hybrid energy storage system. It does not require the special integration of other heating devices or dedicated circuits, and therefore has the advantages of low cost and ease of use. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0024] Figure 1 Schematic diagram of a first typical configuration of a hybrid energy storage system in an embodiment of the present invention;

[0025] Figure 2 Schematic diagram of a second typical configuration of a hybrid energy storage system in an embodiment of the present invention;

[0026] Figure 3 Flow chart of the self-heating method in an embodiment of the present invention.

[0027] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0030] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0031] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0033] Example 1

[0034] This embodiment discloses a hybrid energy storage system with a low-temperature self-heating function, including a battery and a supercapacitor connected in parallel on a bus, and the battery and the supercapacitor are connected in parallel through a bidirectional DC / DC converter, so that the battery and the supercapacitor can be charged and discharged with each other to complete the low-temperature self-heating of the battery. Wherein, the battery is a lithium battery. The lithium battery is used as an energy device of the hybrid energy storage system, and the supercapacitor is used as a power device of the hybrid energy storage system. The bidirectional DC / DC converter can be controlled by pulse width modulation to enable high-frequency mutual charging and discharging between the lithium battery and the supercapacitor to achieve low-temperature self-heating of the battery. It has the characteristics of fast temperature rise rate and high energy efficiency, and is suitable for the inherent configuration of the hybrid energy storage system. There is no need to specially integrate other heating devices or dedicated circuits, so it also has the advantages of low cost and ease of use.

[0035] refer to Figure 1-2 , which are two typical semi-active configurations of hybrid energy storage systems. Figure 1 In actual operation, the hybrid energy storage system configuration can control the bidirectional DC / DC converter through pulse width modulation signals, thereby realizing real-time output / input power distribution of lithium batteries and supercapacitors and energy management of the entire hybrid energy storage system. Figure 2 The hybrid energy storage system configuration in Figure 1 The combination of the configuration and the passive configuration, when the semiconductor switch is turned off and the DC / DC converter is turned on, Figure 1 The configuration is the same; when the conductive semiconductor is turned on and the DC / DC bidirectional converter is disconnected, it becomes a passive hybrid energy storage configuration. At this time, the output / input power distribution of the lithium battery and supercapacitor is completely determined by the electrical characteristics of the device itself.

[0036] When the outside temperature is too low (such as -40 degrees Celsius), the lithium battery has a large impedance, which makes it difficult to charge and discharge normally, causing the performance of the entire hybrid energy storage system to drop sharply. However, conventional external heating methods such as heat conduction or convection have the disadvantages of slow temperature rise rate and low energy efficiency, and are not effective in some special scenarios. Figure 1-2 In the typical configuration, since the bidirectional DC / DC can not only perform real-time power distribution, it can also be used to realize the mutual charging and discharging between lithium batteries and supercapacitors, and the use of appropriate high-frequency AC to stimulate the battery can quickly heat up the inside of the battery through Joule heat. Figure 1 In this configuration, the lithium battery and the supercapacitor can be considered to be connected in parallel through a bidirectional DC / DC. Therefore, after disconnecting the hybrid energy storage system from the bus, the bidirectional DC / DC can be controlled by pulse width modulation to allow the battery and the supercapacitor to charge and discharge each other. Figure 2In this configuration, when heating is required, the semiconductor switch can be disconnected first, and the lithium battery and the supercapacitor can also be regarded as being connected in parallel through a bidirectional DC / DC, and then the bidirectional DC / DC is controlled by pulse width modulation to enable mutual charging and discharging between the battery and the supercapacitor.

[0037] In this embodiment, a temperature sensor is provided on the surface of the battery to measure the real-time temperature of the battery.

[0038] Example 2

[0039] For the hybrid energy storage system with low-temperature self-heating function in Example 1, this embodiment discloses a self-heating method, which can preheat the entire system in the hybrid energy storage system in Example 1 under a low-temperature environment, referring to Figure 3 After the entire hybrid energy storage system is started, the self-heating method specifically includes the following steps:

[0040] Step 1, when the hybrid energy storage system is started, the actual temperature of the battery is obtained, and it is determined whether the temperature of the battery is lower than the preset temperature. If so, the bus is disconnected and heated, that is, step 2 is entered; otherwise, the bus is connected and the system works normally;

[0041] Step 2, determining the optimal frequency of the battery self-heating AC excitation current based on the real-time temperature of the battery;

[0042] Step 3, controlling the bidirectional DC / DC converter by pulse width modulation, so that the battery and the super capacitor perform high-frequency mutual charging and discharging, wherein the current at the battery end during the mutual charging and discharging process between the battery and the super capacitor is the battery self-heating AC excitation current in step 2, and the battery self-heating AC excitation current is controlled to an optimal amplitude during the mutual charging and discharging process between the battery and the super capacitor;

[0043] Step 4, after a preset period of time, the actual temperature of the battery is obtained again, and it is determined whether the temperature of the battery is lower than the preset temperature. If so, return to step 2, otherwise, the bus is connected and the system works normally.

[0044] It should be noted that after the hybrid system is working, generally speaking, its temperature will not drop, because the system will release heat when working and has insulation measures; therefore, the self-heating method in this embodiment is mainly used for cold start. Of course, if the battery temperature of the hybrid energy storage system is lower than the preset temperature when working, it is also possible to consider disconnecting the bus to heat it, that is, entering the above step 2.

[0045] In step 2, the optimal frequency of the AC excitation current corresponding to the real-time temperature of the battery is obtained by calibrating the battery in advance. In this embodiment, the calibration process of the optimal frequency is specifically as follows:

[0046] Step 2.1, define the temperature range in which the battery needs to be self-heated by AC, for example, the temperature range is [T A ,T B ], where the right end point of the temperature interval is T B This is the preset temperature in step 1, T A Can take -80℃;

[0047] Step 2.2, select a number of temperature sampling points in the temperature range, for example, select N temperature sampling points, {T i ∈[T A ,T B ]|i=1,2,…,N}; and select several different charge states of the battery, for example, select M different charge states, {SOC j |j=1,2,…,M}. For each temperature sampling point, perform the following operations:

[0048] When the battery is at the temperature corresponding to the temperature sampling point T i When the battery is tested in the frequency range of AC excitation current [ω A ,ω B The impedance Z at each frequency and charge state within ] j (ω), for every frequency ω∈[ω A ,ω B ], and calculate the corresponding impedance {Z j (ω)|j=1,2,…,M}, the frequency with the smallest difference less than the preset difference value is selected as the optimal frequency of the AC excitation current of the battery at the corresponding temperature sampling point. In this embodiment, the relative standard deviation std(Real(Z j (ω))) / mean(Real(Z j (ω))) is used to measure the difference, that is, the optimal frequency ω* needs to satisfy:

[0049] ω*=min ω {std(Real(Z j (ω))) / mean(Real(Z j (ω)))}

[0050] It should be noted that in addition to the real part of the impedance, a variety of indicators or formulas can be selected to measure different charge states SOC jThe corresponding impedance value differences should all fall within the protection scope of the parameter selection method in this embodiment. The principle of using the above calibration to determine the optimal frequency is: the polarization process corresponding to the Faraday current inside the lithium-ion battery is a charge transfer reaction, and the impedance data corresponding to the polarization process is related to the battery charge state; and correspondingly, the impedance data corresponding to the polarization process of the non-Faraday current inside the lithium-ion battery is independent of the charge state; therefore, by analyzing whether the impedance value is related to the charge state at a specific frequency, it can be determined whether the polarization process corresponding to the frequency is related to the Faraday current. And because the optimal frequency determined by the above calibration has a standard deviation less than the preset value, it can be determined that its impedance value is basically independent of the charge state, so it can be considered that the polarization process at the optimal frequency will not produce obvious Faraday current. Therefore, at the current temperature T i Under this condition, using AC excitation higher than this characteristic frequency to heat the battery will not cause lithium plating and aging.

[0051] Step 2.3, interpolate the optimal frequency of the AC excitation current corresponding to each temperature point and each temperature sampling point in the temperature range to obtain the battery temperature-AC excitation current optimal frequency curve; finally, based on the real-time temperature of the battery and the battery temperature-AC excitation current optimal frequency curve, the optimal frequency of the current battery self-heating AC excitation current can be obtained.

[0052] In step 3, the specific implementation of controlling the battery self-heating AC excitation current to the optimal amplitude during the mutual charging and discharging process between the battery and the supercapacitor is as follows: during the mutual charging and discharging process between the battery and the supercapacitor, the amplitude of the battery self-heating AC excitation is gradually increased from 0, and the upper limit of the battery terminal voltage reaches the charging cut-off voltage V c Or the lower limit reaches the discharge cut-off voltage V d As a preferred embodiment, a voltage margin δ can be set at the optimal excitation amplitude of the battery AC self-heating, that is, when the upper limit of the battery terminal voltage reaches the charging cut-off voltage minus the voltage margin (i.e., V c -δ) or the lower limit reaches the discharge cut-off voltage plus the voltage margin (i.e. V d +δ), the AC excitation current amplitude at this time is the optimal excitation amplitude for battery AC self-heating.

[0053] In step 4, the preset time period can be set to 30-60 seconds, that is, steps 1-3 are performed again every 30-60 seconds during the self-heating process, so that the optimal frequency and optimal amplitude of the battery self-heating AC excitation current can be updated with the real-time temperature of the battery.

[0054] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A self-heating method for a hybrid energy storage system with a low-temperature self-heating function, characterized in that: The hybrid energy storage system includes a battery and a supercapacitor connected in parallel on a bus, and the battery and the supercapacitor are connected in parallel through a bidirectional DC / DC converter, so that the battery and the supercapacitor can be charged and discharged mutually, and the low-temperature self-heating of the battery is completed. The self-heating method includes the following steps: Step 1, when the hybrid energy storage system is started, the actual temperature of the battery is obtained, and it is determined whether the temperature of the battery is lower than the preset temperature. If so, the bus is disconnected and heated, that is, step 2 is entered; otherwise, the bus is connected and the system works normally; Step 2, determining the optimal frequency of the battery self-heating AC excitation current based on the real-time temperature of the battery, specifically: Define the temperature range in which the battery needs to be AC ​​self-heated, where the right end point of the temperature range is the preset temperature in step 1; Select several temperature sampling points in the temperature range and select several different charge states of the battery. Perform the following operations for each temperature sampling point: When the battery is at a temperature corresponding to a temperature sampling point, the impedance of the battery is tested at each frequency and each charge state within the frequency range of the AC excitation current. For each frequency, the difference in impedance at each corresponding charge state is calculated, and the frequency with a difference less than a preset difference value and the smallest difference is selected as the optimal frequency of the AC excitation current of the battery at the corresponding temperature sampling point; According to each temperature adoption point and the optimal frequency of the AC excitation current corresponding to each temperature sampling point, interpolation is performed in the temperature range to obtain a battery temperature-AC excitation current optimal frequency curve; Based on the real-time temperature of the battery and the battery temperature-AC excitation current optimal frequency curve, the optimal frequency of the current battery self-heating AC excitation current can be obtained; Step 3, controlling the bidirectional DC / DC converter by pulse width modulation, so that the battery and the super capacitor perform high-frequency mutual charging and discharging, wherein the current at the battery end during the mutual charging and discharging process between the battery and the super capacitor is the battery self-heating AC excitation current in step 2, and the battery self-heating AC excitation current is controlled to an optimal amplitude during the mutual charging and discharging process between the battery and the super capacitor; Step 4, after a preset period of time, the actual temperature of the battery is obtained again, and it is determined whether the temperature of the battery is lower than the preset temperature. If so, return to step 2, otherwise, the bus is connected and the system works normally.

2. The self-heating method according to claim 1, characterized in that: The battery surface is provided with a temperature sensor for measuring the real-time temperature of the battery.

3. The self-heating method according to claim 1, characterized in that: In step 3, the battery self-heating AC excitation current is controlled to an optimal amplitude during the mutual charging and discharging process between the battery and the supercapacitor, specifically: During the mutual charging and discharging process between the battery and the supercapacitor, the amplitude of the battery self-heating AC excitation is gradually increased from 0. When the upper limit of the battery terminal voltage reaches the charging cut-off voltage or the lower limit reaches the discharging cut-off voltage, the amplitude of the AC excitation current is the optimal amplitude.

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